The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
Currently a typical free flight rocket, comprised of a warhead and a motor, spins the entire rocket assembly in the same direction and has a relatively high moment of inertia. At motor burn-out, the rocket undergoes an abrupt reversal of spin direction. This reversal, caused by an aerodynamic torque from the fins, creates a perturbation in the rocket trajectory, making the trajectory erratic. A more predictable trajectory and thus greater accuracy in the rocket aim would be achieved if the spin of the warhead could be separated from the spin of the motor at the time of motor burn-out. Such separation would reduce the effective roll inertia of the rocket and enable the warhead, and thus the entire rocket, to maintain the original trajectory.
Rocket Accuracy Improvement Device 102, when coupled between warhead 103 and motor 101 of a typical free flight rocket 100, isolates the warhead from the rocket motor in the roll axis using a plurality of ball bearings and thereby enables the warhead to spin independently of the motor. This reduces the effective roll inertia of the rocket at the time of spin reversal at motor burn-out. Further, the separation of the warhead from the motor allows the efficient rapid initial spin-up of just the motor during motor boost. This rapid initial spin-up reduces the effects of thrust misalignment and rocket imbalance that are largely responsible for rocket dispersion, thus setting the rocket on a more accurate trajectory at the start.
During the powered stage of the rocket flight, a portion of the motor spin is transferred to the warhead due to the bearing drag torque, with the warhead reaching its maximum spin rate at the time the motor burns out. Therefore, even when the motor reverses its spin, the angular momentum of the warhead tends to act gyroscopically to maintain the trajectory of the rocket, thus achieving a much more predictable flight path for the rocket.